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    <title>Document</title>
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    <div>asdfasdfasdf</div>
    <DIV>ASDFASDFASDFASDF</DIV>

    <div data-cardId="654654654654654645646466">必踩的坑</div>

    <script>
        // 变量 a 和 A 是两个不相同的变量
        var a = 100;
        var A = 200;

        // 驼峰式命名: 小写字母开头,第二个单词首字母大写
        var cartId;
        var cartList;

        // 关键字和保留字,使用了就会报错
        var continue;
        var if;

    </script>
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